The present invention relates to an impact absorbing member and, particularly to an impact absorbing member which is suitably adapted to absorb impact energy exerted on the head of an occupant in a vehicle cabin to reduce the head injury criteria value in the event of a vehicle collision.
The followings are impact absorbing members for use in vehicles which have been conventionally proposed.
(1) An impact absorbing member comprises a resin pillar garnish having a hollow shape wherein a hollow is filled with rigid polyurethane foam for absorbing impact energy (Japanese Patent H06-42437A).
(2) A pad member is made of foamed material or rubber material (a prior art description of Japanese Patent H08-2358A).
(3) A cushion body is made of rigid polyurethane foam and is covered by a shape keeping member of sheet metal having a recess formed therein (Japanese Patent H08-72642A).
(4) An impact absorbing member is provided by using a garnish (trim) (Japanese Patent H06-211088A).
(5) An impact absorbing member is made of resin beads and has a number of ribs formed on one surface (Japanese Patent H07-16867A).
(6) An impact absorbing member is constituted of a polyolefin resin material which has ribs arranged in a lattice shape (Japanese Patent H08-142234A, Japanese Patent H08-295194A).
The aforementioned conventional impact absorbing members have the following drawbacks, respectively.
The impact absorbing member disclosed in Japanese utility model H06-42437A uses the rigid polyurethane foam as the head protective material. However, it has a structure complex with the hollow resin piece (garnish). Therefore, the rigid polyurethane foam is required to have low compressive strength of 0.02 to 0.2 MPa. This means that this does not take advantage of characteristics of the rigid polyurethane foam. The purpose of its concave and convex shape is just to reduce the weight and to keep the strength, and not to improve the energy absorbing capacity. Therefore, this does not have improved energy absorbing capacity.
The impact absorbing member disclosed as a prior art of Japanese Patent H08-2358A is an example of a pad member for absorbing impact made of foamed material or rubber material. In this example, the pad member is elastically deformed and thus does not suggest the usage of rigid polyurethane foam. Portions of a corrugated section attached to a vehicle body are extremely thin. To obtain sufficient energy absorbing capacity, the thickness of the pad member should be large. Accordingly, the cabin space of the vehicle is reduced, thus worsening the comfort, the facility of riding, and further the visibility.
The impact absorbing structure disclosed in Japanese Patent H08-72642A has a concave shape as a whole, but a soft or rigid polyurethane form itself used as crushing material does not have a recess for improving the energy absorbing capacity. The purpose of a recess formed in the impact absorbing structure is just installation, not improvement of the energy absorbing capacity. In this publication, it is stated that it can not exhibit sufficient energy absorbing efficiency if the entire rigidity is too high or too low. However, there is no description about specific value and range. It is hard to say that this impact absorbing structure securely exhibits excellent energy absorbing efficiency.
The impact absorbing member disclosed in Japanese Patent H06-211088A has a structure to be fixed together with a garnish to a vehicle body by fasteners so that the garnish is necessary for installation of this impact absorbing member. For utilizing the impact absorbing member as a head protective member, the location adaptability is limited, for example, it is not suitably adapted to a side rail. The impact absorbing member does not have a concavity or convexity. Though it is stated that the impact absorbing member has such a thickness as to absorb impact energy, there is no description about specific thickness and hardness. It is also hard to say that the impact absorbing member securely exhibits excellent energy absorbing efficiency.
The impact absorbing member disclosed in Japanese Patent H07-16867A is made of resin beads. When a force is locally exerted on a surface of the impact absorbing member by a spherical body such as a head dummy, the force focuses on beam portions between the ribs, thus not obtaining sufficient impact absorbing capacity. If the impact absorbing member having the aforementioned configuration is made of rigid polyurethane foam, the beam portions may be broken, thus not obtaining sufficient stroke for absorbing impact energy.
According to the impact absorbing member disclosed in Japanese Patent H08-142234A and Japanese Patent H08-295194A, the thickness of the lattice-shaped ribs is small such as 0.6 to 1.2 mm. In addition, since the ribs made of polyolefin resin material absorbs energy generally by the bending of the ribs, the impact absorbing member has a drawback that the capacity has high dependence of the direction of impact.
As mentioned above, any one of the aforementioned conventional impact absorbing members is not the one whose configuration is positively devised to obtain the optimal energy absorbing capacity. Accordingly, high energy absorbing capacity can not be imparted to these impact absorbing members.
On the other hand, at pillars and side rails in an automobile, the dimension in thickness has a greater effect on the comfort in the cabin and the visibility for the safety. To reduce the head injury criteria value to protect the occupant without impairing these factors, an impact absorbing member is required which is thin, but can exhibit sufficient energy absorbing efficiency.
As an impact absorbing member for use in vehicles which can solve the aforementioned problems and which has excellent energy absorbing capacity and is suitably adapted to absorb impact energy exerted on the head of an occupant in a vehicle cabin to reduce the head injury criteria value in the event of a vehicle collision, an impact absorbing member has been previously proposed by the applicant of this application, which has a plate-like configuration and is made of rigid polyurethane foam having compressive strength of a predetermined value or more, and which has recesses formed in at least one surface thereof (Japanese Patent 2000-6741A) published on Jan. 11, 2000, a corresponding European application of which is EP 967124 A2 published on Dec. 29, 1999.
In this impact absorbing member, walls between adjacent recesses of the impact absorbing member made of rigid polyurethane foam are broken to absorb impact energy. The broken walls sequentially enter the recesses, thereby obtaining stable energy absorbing capacity. The entrance of the walls into the recesses provides the stroke for absorbing energy, thereby sufficiently reducing the head injury criteria value suffered by an occupant.
In this impact absorbing member, it is preferred that the ratio of the volume of the recesses to the sum of the volume of solid portions made of the rigid polyurethane foam and the volume of the recesses (hereinafter, sometimes referred to as xe2x80x9crecess volume ratioxe2x80x9d) is 10 to 40%.
Therefore, the object of the present invention is to provide an impact absorbing member for use in vehicles which is an improvement over the impact absorbing member of Japanese Patent 2000-6741A and which has excellent energy absorbing capacity and is suitably adapted to absorb impact energy exerted on the head of an occupant in a vehicle cabin to reduce the head injury criteria value in the event of a vehicle collision.
An impact absorbing member of the present invention is made of rigid polyurethane foam and has a plate-like shape, and includes recesses formed in at least one surface thereof to be arranged in parallel along one direction, wherein each recess is formed in such a shape as to have sectional area decreasing toward the deepest point.
It is preferable that the shape of each recess is acute at the bottom in the depth direction of the impact absorbing member.
The inventors of this application made efforts for improving the energy absorbing capacity of the impact absorbing member disclosed in Japanese Patent 2000-6741A. As a result of their efforts, they found that the impact absorbing member formed with recesses having such a shape decreasing toward the bottom in the depth direction of the impact absorbing member, for example having a triangular section along the depth direction of the impact absorbing direction, has higher energy absorbing capacity as compared to the impact absorbing member formed with recesses each having rectangular section even with the same recess volume ratio. This means that the impact absorbing member formed with such recesses can be effectively used for reducing the head injury criteria value. By this finding, the present invention was accomplished.
It should be noted that a recess having an acute bottom in the depth direction of the impact absorbing member of the present invention will be sometimes referred to as xe2x80x9cacute-bottom recessxe2x80x9d. In the present invention, the xe2x80x9ctrianglexe2x80x9d on the section view of the recess has the apex angle at the deeper side of the recess.
According to the present invention, the compressive strength of the rigid polyurethane foam constituting the impact absorbing member is preferably 3xc3x9710xe2x88x921 MPa or more to effectively exhibit the impact energy absorbing efficiency by the breakage of the rigid polyurethane foam portion between the recesses and also the impact energy absorbing efficiency or capacity by the entrance of the broken portion into the recesses.
According to the present invention, it is preferable that the recess volume ratio (the ratio of the volume of the recesses to the total of the volume of the rigid polyurethane foam portion and the volume of the recesses of the impact absorbing member) is 3 to 40%.
When the impact absorbing member has a shape lengthwise in one direction, the recesses are preferably formed in a portion other than both end portions of the impact absorbing member.
The impact absorbing member of the present invention having the aforementioned construction is suitably used as a head protective member for use in vehicles in a state attached to a vehicle body or an interior equipment such as a head liner and a garnish.
A head protective member of the present invention is formed in a lengthy rectangular shape and is constituted of a rigid polyurethane foam having hardness of 0.3 MPa or more, a thickness of the head protective member is 15 to 25 mm and the effective width of portions mainly absorbing impact is 30 to 40 mm.
In the present invention, the hardness of material is measured by the following steps (i)-(iii).
(i) A sample having a thickness 50 mmxc3x97a width 50 mmxc3x97a length 50 mm (if this size is not obtained, an available size may be applied) is prepared from the material.
(ii) This sample is compressed at a speed of 10 to 50 mm/min in a direction of thickness for a distance of 80% of the original thickness (for a distance of 40 mm when the sample is 50 mm in thickness, i.e. to be 10 mm).
(iii) The load when the sample is compressed to be 50% of the original thickness (25 mm of the sample is compressed if the sample is 50 mm in thickness) is measured. The hardness (MPa, N/cm2) is obtained by dividing the measured load by the sectional area.
When the head protective member has no slit, the effective width is equal to the actual width of the head protective member. When the head protective member has a slit, the effective width is the sum of widths of solid portions having hardness of 0.3 MPa. It should be noted that the effective width of portions mainly absorbing impact of the head protective member of the present invention is referred to just as xe2x80x9ceffective widthxe2x80x9d.
According to the head protective member which is constituted of a rigid polyurethane foam having hardness of 0.3 MPa or more, the thickness of the head protective member is 15 to 25 mm and the effective width is 30 to 40 mm, the HIC value is 800 or less, by which excellent energy absorbing capacity can be achieved.
The HIC value means the head injury criteria value (HIC (d)) calculated from acceleration of impact exerted on a dummy in dynamic evaluation tests using dummies. In general, the HIC value of 1000 or less indicates excellent energy absorbing capacity. In car manufacturers, developments are made to have a HIC value of 800 or less for the purpose of increasing the certainty.
A head protective member of the present invention has, for example, a slit formed in the head protective member by hollowing in the depth direction to extend in the longitudinal direction, such that the sum of widths of solid portions other than the slit is set to be 30 to 40 cm. In this case, it is preferable that the width of the slit is 5 to 20 cm. In addition, it is preferable that the hardness of the material constituting the head protective member is 1.2 to 1.6 MPa.
The head protective member may have a plate-like body without having a slit formed by hollowing in the depth direction. In this case, it is preferable that the hardness of the material constituting the head protective member is 1.0 to 1.4 MPa.
The head protective member is suitably used in a vehicle in a state attached to a vehicle body or an interior equipment such as a head liner and a garnish.